1. Field of the Invention
The present invention relates to an electrical traction system notably for automobiles that is, in particular, a multifunction system integrating the main motor and brake generator function with the auxiliary charger and converter functions. It also relates more particularly a self-synchronous electrical motor that can be used notably in electrical traction systems for automobiles.
It is recalled that a self-synchronous motor is a motor in which there is produced a magnetic field rotating exactly at the same speed as the rotor, whatever may be this speed, i.e. especially when it is starting.
In the field of the technology of electrical traction systems for automobiles, there is the major problem of reducing the quantity and cost price of the raw material used as well as the number of electronic components used for the controls.
The aim of the present invention therefore is to provide an electrical traction system for automobiles that meets practical requirements more efficiently than do prior known traction systems of the same type, designed for the same purpose, notably inasmuch as this system is:
lighter, PA1 less costly, PA1 more efficient, PA1 more reliable, PA1 at least one electrical generator, notably an electromechanical generator (constituted, in this case, by a thermal motor for the driving of a generator, especially an AC generator) and/or an electrochemical generator, constituted by at least one accumulator and/or at least one fuel cell; PA1 at least one electrical machine that is reversible (namely a machine capable of working as a motor and brake generator and hence capable of carrying out notably the function of electrical traction in motor operation) said electrical machine being of the self-synchronous type, comprising: PA1 at least one charger carried in the system, said charger being designed to recharge at least one main supply battery (Vp); PA1 at least one converter of the high-voltage direct current, corresponding to said main supply battery (Vp), into a low-voltage direct current designed for the supply and recharging of a standard auxiliary battery (Vs), the voltage of which is notably 6 V or 12 V, PA1 the stator comprises star-connected first, second, third and fourth windings (E1, E2, E3, E4) that are spatially offset by 90/p mechanical degrees (2p being the number of magnetic poles of the self-synchronous machine) and are connected two by two so as to define a first group and a second group of windings (E1, E2, E3, E4), of which the first group comprises said first and third stator windings (E2, E3) while the second group comprises said second and fourth windings (E2, E4) so that the windings (E1, E3) of said first group as well as the windings (E2, E4) of said second group are offset with respect to one another by 180 electrical degrees while the first and second windings (E1, E2) as well as the third and fourth windings (E3, E4) are offset with respect to one another by 90 electrical degrees; PA1 the above-mentioned commutation means comprise first, second, third and fourth choppers (a, A, b, B) that are mounted in series respectively with said first, second, third and fourth windings (E1, E2, E3, E4) and are controlled sequentially two by two (a, A; b, A; b, B; a, B) b, B) during commutation, i.e. the commutation of the first and second choppers (a, A) is actuated, then the commutation of the third and second choppers (b,A) as well as that of the third and fourth choppers (b, B), and this is followed by the commutation of the first and fourth choppers (a, B), to enable the sequential shunting or routing of the stator current (Ist) in the stator windings combined two by two, i.e. respectively in the first and second windings (E1, E2), the third and second windings (E3, E2), the third and fourth windings (E3, E4), as well as in the first and fourth windings (E1, E4), said second and fourth choppers being also controlled in modulation to set the value of said stator current. PA1 in motor operation, said second and fourth choppers (A, B) are respectively protected by a first diode and a second diode, known as "free wheel" diodes (d1, d2) each connected in parallel with said first and second windings (E1, E2) and, respectively, said third and fourth windings (E3, E4); PA1 in generator operation, the reversal of the direction of flow of the current in the stator windings (E1, E2, E3, E4), with respect to the direction of flow of the current in motor operation, is controlled respectively by a third diode and a fourth diode (d3, d4) each series connected with said second winding (E2) and, respectively, said fourth stator winding (E4); PA1 the rotor current (Iro) in the rotor winding (E5) is controlled by a fifth one-way chopper (C) protected by a fifth diode (d5). PA1 the means for commutation from the motor/brake generator operation to the charger operation comprise: PA1 wherein said contacts (c1 to c5) make it possible to change the connections between the stator windings (E1, E2, E3, E4) and the corresponding electronic components in such a way that when said contacts work in the direction corresponding to the charger operation, they enable, by the opening of the first, second and third contacts (c1, c2, c3), firstly the series connection of said third and fourth stator windings (E3, E4) to each other to constitute the primary winding of a transformer and, secondly, the series connection of said first and second windings (E1, E2) to each other to constitute the secondary winding of said transformer while, by the closing and opening respectively of said fourth and fifth contacts (c4, c5), said first, second, third and fourth diodes (d1, d2, d3, d4) are connected to one another in such a way as to constitute the elements of a rectifier bridge that is connected to said secondary winding (El +E2) of the transformer and is designed to recharge the main battery, when the electromotive force is greater than the supply voltage; PA1 wherein the charging current of this battery is controlled in the primary winding (E3+E4) of said transformer by sixth and seventh choppers (D, E); and PA1 wherein a sixth contact (c6) which works in a closed state in motor operation mode and hence in an open state in the charger operation mode, provides, in conjunction with said second, third and fifth contacts (c2, c3, c5), for the insulation of the primary winding of the transformer from the secondary winding of said transformer, and hence insulates the mains supply from the battery (Vp).
and at the same time meets regulatory standards and especially safety standards. The invention is also aimed more generally at improving electrical motors by reducing their cost.
The solution to the technical problem referred to here above is defined by means for the commutation of the stator windings of the electrical motor of the electrical traction system that is an object of the present invention enabling the performance by these same windings, as required, not only of their main motor/generator function but also of the auxiliary charger and/or converter functions.
2. Description of the Prior Art
Known self-synchronous motors comprise generally star-connected stator windings that are series-connected with electronic switches. These switches are activated at a frequency (that can be called a high frequency) which is far higher than the electrical frequency of the rotating magnetic fields generated at the stator; the (low) frequency of the rotating magnetic fields corresponds to the speed of rotation of the motor. The switches are used to chop the current at high frequency with a cyclical ratio that is variable so that it is possible, firstly, to control the value of the mean current in the stator windings during periodic time intervals (low frequency) when a current effectively flows in these windings and, secondly, to totally interrupt this current during other periodic time intervals (low frequency). With several stator windings and, hence, several electronic switches, it is possible to shunt or route the current successively (at low frequency) into the windings so as to create a rotating stator magnetic field. The envelope of variation of the mean current in a winding is defined by the variation of the cyclical ratio of the chopped current, which can be adjusted at will as a function of the waveform desired for the mean current. These self-synchronous motors use at least as many electronic switches as windings, and these electronic switches are costly especially if high currents go through them, which is the case with automobiles. The present invention is aimed at reducing the cost of the motor and increasing its reliability without lowering its performance characteristics.